1. Technical Field
The present disclosure relates to a red phosphor material that can be used for light-emitting devices such as light sources of projectors, light sources of vehicle-mounted head lamps, and light sources of white LED lighting apparatuses, the red phosphor material being used in combination with, for example, a light-emitting diode (LED) or a semiconductor laser diode (LD). The present disclosure also relates to a light-emitting device including the red phosphor material.
2. Description of the Related Art
Lighting apparatuses employing white LEDs have higher efficiency and longer longevity than existing lighting apparatuses. From the standpoint of resource savings and energy conservation, such lighting apparatuses have come to be widely introduced for commercial use and home use.
Most commonly used white LEDs include a blue LED chip and a phosphor substance that partially absorbs blue light emitted by the LED chip and emits yellow light. This configuration causes mixing of blue light and its complementary-color light, that is, yellow light, resulting in generation of a pseudo-white color. There is ongoing development of other white LEDs employing a combination of a blue LED chip, a green phosphor substance, and a red phosphor substance in order to meet requirements in terms of color rendering, color reproducibility, or the like. There is also ongoing development of still other white LEDs employing a combination of an LED chip emitting light in the near ultraviolet to blue violet region and three phosphor substances that are a blue phosphor substance, a green phosphor substance, and a red phosphor substance.
For applications including light sources of projectors and light sources of vehicle-mounted head lamps, which require high emission energy, there is ongoing development of light sources employing a combination of an LD emitting light in the near ultraviolet to blue violet region and a phosphor substance.
A known red phosphor substance that can be excited with light ranging from near-ultraviolet light to blue light is a phosphor substance that is represented by the composition formula Ca2-2xLixEuxW2O8 and that emits light in the red color region with Eu3+ serving as the luminescent center (for example, refer to Japanese Unexamined Patent Application Publication Nos. 2007-254517, 2008-7644, and 2010-229388).